Diffraction of Light
Diffraction is the phenomenon of the bending and spreading of light waves around the edges of an obstacle or through a narrow aperture when the size of the obstacle or aperture is comparable to the wavelength of light.
It is a clear demonstration of the wave nature of light and occurs due to the superposition and interference of secondary wavelets.
Types of Diffraction
Diffraction is mainly of two types:
1. Fresnel Diffraction
In Fresnel diffraction, the source and the screen are at finite distances from the diffracting obstacle or aperture. The incident wavefront is generally spherical or cylindrical.
Examples:
- Diffraction by a straight edge
- Diffraction by a narrow slit
- Diffraction by a circular aperture
2. Fraunhofer Diffraction
In Fraunhofer diffraction, the source and the screen are effectively at infinite distances from the diffracting aperture or obstacle. In practice, lenses are used to produce parallel incident and diffracted wavefronts.
Examples:
- Single-slit diffraction
- Double-slit diffraction
- Diffraction grating
Difference Between Fresnel and Fraunhofer Diffraction
| Fresnel Diffraction | Fraunhofer Diffraction |
|---|---|
| Source and screen are at finite distances | Source and screen are effectively at infinite distances |
| Incident wavefront is spherical or cylindrical | Incident wavefront is plane |
| No lenses are generally required | Lenses are generally used |
| Pattern depends on distance | Pattern is comparatively simpler |
| Analysis is more complex | Analysis is easier |